A polycarbonate resin has been used as a material for molded products in various industrial fields because of its excellent mechanical characteristics, thermal characteristics and electrical characteristics. Recently, the polycarbonate resin has often been used in a field of a functional product requiring optical characteristics of the polycarbonate resin as well as the above characteristics. With such an expansion of the field in which the polycarbonate resin is used, required performances of the polycarbonate resin become diversified. Accordingly, not only a conventionally used polycarbonate resin but also a polycarbonate resin having various chemical structures have been proposed.
The functional product is exemplified by an organic electrophotographic photoreceptor in which the polycarbonate resin is used as a binder resin for functional materials such as a charge generating material and a charge transporting material.
Depending on electrophotography process to be applied, the organic electrophotographic photoreceptor is required to have predetermined sensitivity, electrical characteristics and optical characteristics. A surface of a photosensitive layer of the electrophotographic photoreceptor is repeatedly subjected to operations such as corona electrification, toner development, transfer onto papers, cleaning and the like. Electrical and mechanical external-forces are applied on the surface of the photosensitive layer every time such operations are performed. Accordingly, the photosensitive layer provided on the surface of the electrophotographic photoreceptor is required to have durability against these external forces in order to maintain electrophotography image quality for a long period of time. Moreover, since the organic electrophotographic photoreceptor is typically manufactured by dissolving the binder resin as well as the functional material in an organic solvent and film-casting the obtained solvent on a conductive substrate and the like, the binder resin is required to have solubility in the organic solvent and stability of the obtained solvent.
Conventionally, a polycarbonate resin made from 2,2-bis(4-hydroxyphenyl)propane, 2,2-bis(4-hydroxyphenyl)cyclohexane and the like have been used as the binder resin for the electrophotographic photoreceptor. However, such a polycarbonate resin is insufficient in durability. It is conceivable that a possible solution for improving the durability is to improve wear resistance of the photosensitive layer. A polycarbonate copolymer has been known as an effective material for improving the wear resistance of the photosensitive layer (see, for instance, Patent Literatures 1 to 3).
A resin disclosed in Patent Literature 1 includes a polycarbonate copolymer manufactured by copolymerizing a component having a bisphenol Z skeleton that contributes to solubility with a component having a biphenol skeleton that contributes to wear resistance. This polycarbonate copolymer is found to have a wear resistance superior to that of a bisphenol-Z-type polycarbonate homopolymer.
Patent Literatures 2 and 3 each disclose a polycarbonate copolymer obtained by copolymerizing a skeleton derived from an oligomer having a small number of monomer units of a biphenol compound with a biphenol skeleton different from the above biphenol skeleton and having a favorable wear resistance, at a copolymerization ratio from 25 mol % to 50 mol %.
Patent Literatures 4 and 5 each disclose a copolymerized polycarbonate resin having a diphenylether skeleton.